My little guy totally eats dirt and sand, so I'm used to seeing actual dirt in the diaper!
Is it dark in color? I was told once when my dd got a bloody nose that swallowed blood could come out looking like dark coffee grounds in the diaper. I don't think it's necessarily a cause for alarm, especially if it just happened once.
Wife to a wonderful dh and mom to four beautiful kiddos, dd (3/04):, ds1 (1/06), ds2 (10/08), and ds3 (7/10)